Several disorders of the eye and brain can cause extensive loss of peripheral vision before affecting the central vision. These include conditions such as glaucoma, cerebrovascular disease and pituitary tumours (Harrington, 1981). The measurement of the distribution and depth of peripheral visual defects is very useful in the diagnosis and management of such conditions (Keltner et al, 1983).
Perimetry has long been established as a useful method of recording visual function, measuring light sensitivity throughout a defined portion of the visual field and determining the position and extent of all areas of reduced visual perception (Harrington et al, 1981). The normal monocular visual field extends to over 100 degrees, but it is often sufficient to test only the central 30 degrees (Schulzer et al, 1987, Weber et al, 1986). In conventional methods of perimetry the subject's eye is fixed on a central stationary target while stimuli are presented at predetermined points in the visual field. However, there is a natural tendency for individuals to look away from the fixation point towards the test stimulus in an attempt to improve the test result. A skilled examiner and/or expensive equipment with considerable co-operation from the patient are all required to ensure that the eye remains immobile throughout the test. Despite these measures, many patients, particularly young children, the elderly and those with neurological deficits, are unable to keep the eye still for long enough and the test has to be abandoned. Failure may also result from loss of interest due to the repetitive nature of the test. Our previous U.S. Pat. No. 4737024 discloses such an oculo-perimetric method and device.
Many automatic visual field tests have been described previously, some using computer graphics (Accornero et al, 1984; Frisen et al, 1986) and other specifically designed for use in children (Fausset et al, 1986). However, none have addressed themselves successfully to the problem of maintaining both fixation and interest whilst keeping the test procedure simple and the equipment inexpensive.
In an effort to mitigate these problems, a method has been developed which allows the subject's eye to move during the procedure and uses the guise of a game to maintain interest.